We upgraded from JBoss 4 (and JDK 5) to JBoss 5 (and JDK 6). The problem is that the start time has gone from 1.5 minutes (on JBoss 4) to more than 4 minutes.
1
I had an issue like this but I found a good improvement by setting the initial and max heap size to same values, I mean:
-Xms512m -Xmx512m
With this, I improved from 4 to 2 minutes the starting time.